CA1072150A - Method of transporting coal, especially for coking purposes, over long distances - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Comminuted coal, in particle sized of about 3 mm and less, is divided into a coarse fraction and a fine fraction, the latter consisting of particle sizes from about 0.4 mm down. The coarse fraction, with particle sizes up to about 3 mm, is transported hydraulically, through a pipeline, to a remote destination to which the fine fraction is delivered dry, e.g. by rail. At the destination the oncoming slurry containing the coarse fraction is mechanically dewatered, as by centrifuging and vacuum drying, the two fractions being then mixed together to provide a mass of coal with an overall moisture content of about 8% suitable for coking. For more efficient hydraulic pumping of the coarse coal fraction through the pipe-line, the slurry may be supplemented by fine-grained ore which is separated therefrom at the destination prior to admixture of the dry-transported fine coal fraction.

Description

SP CIFICATION

l`he present invention relates to a method of trans-porting coal~ especially substarltial quantities of commi-nuted coking coal~ over long distances.

In recent times~ comminuted solids such as coal or ore are transported with increasing frequency-over distances ~; of several hundred k~ilometers (as between production~ trans-shipment and/or utilization sites) via pipelines through which they are pumped with the aid of a carrier fluid~
usually water.

In the feeding of coal to a cokery~ the quality of the coke and the economy of the coking process depend inter alia upon the moisture content and the particle size of the coal employed. Thus ? the water used in the piping of the ` coal must be substantially entirely removed before the ` coking operation.

Whereas the dewatering of relatively coarse par-ticle fractions ( ~ 0.5 mm ) is largely possible with pure-ly mechanical and therefore inexpensive means~ such a process becomes progressively less efficient with increas-ing proportions of particle fractions below 0.5 mm; these latter fractions~ referred to hereinafter as fines~ can be dried in practice only with thermal evaporation which is relatively costly. As is well known~ the overall water content of the coal used for coking should be at about 8%.
This value can be readily reached by mechanical dewatering (centrifugation and vacuum filtering) with coal lacking l ' . . .
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21~8C 107Z150 a particle fraction of less than 0.5 mm~ whereas a like treatment of coal with fines in a proportion of 40% or more leaves a residual water content of about 20~.
The object of the present invention is~ therefore~
` ~to provide a more efficient and economical method of trans-porting large quantities of coal~ ranging in particle size from about 3 mm to 0.~ mm or less~ to a remote destination such as a cokery.
This object i5 achieved~ in accordance with the invention~ by dividing the mass of coal to be transported~
comminuted to particle sizes up to about 3 mm~ into a coarse - fraction and a fine fraction~ the latter fraction contain-ing at least the major part of the particles ranging in size up to about 0.4 mm. The coarse fraction is hydraulic-ally pumped through a pipeline to a remote destination to ., - which the fine fraction is transported independently~ e.g.
by railroad~ in an essentially dry state (i.e. with its "~ . .
natural moisture content).
The fine fraction~ which may account for at least - 20 a fifth o~ the entire coal to be transported~ therefore arrives at its destination with substantially the moisture content of the mine (i.e. with about 6% water). This en-tails the advantage that the dewatering costs for the hy-draulically transported coal are very low since expensive thermal drying processes~ which would be required for the treatment of the fines~ are dispensed wit`n. Thus~ by mixing together the dry fine fraction and the dewatered :
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210c~ 107Z150 coarse fraction~ a coking coal having the desired water content of about ~% can be immediately obtained. The cost reduction resulting frorn the e~imination oE thermal drying~
taking into account the freight costs for the fines at current railroad rates~ is rather substantial.

The admixture of the coarse coal fraction with the necessary amount of water~ sufficient to form a slurry that can be conventionally pumped through a pipeline~ is well known per se and need not be discussed in detail.

The scarcity of fines in the hydraulically trans- -ported coarse fraction~ however~ may in some instances require higher pumping pressures andjor an increased number of pumping stations in the pipeline. Furthermore~ for a more economical utilization of an available pipeline~ it may be desirable to pump not only coal but also other solids through that line~ especially comminuted ore where the line terminates at a foundry equipped with its own - cokery. In such a case the transportation of ore and of -- the coarse coal fraction through one and the same line~
e.g. from a transshipment site such as a seaport~ can proceed~ in a manner known`Per se, by alternately pumping one or the other product. Preferably~ though~ the coarse coal fraction is accompanied by a mass of finely commin- -uted ore -- of a particle size less than that of the ; smallest coal fragments present in significant quanti-ties -- which more or less replaces the fine coal fraction --removed from the original mass so as to form a more readily _~_ - ' - ' . - ' - .

2,~ q&c 107Z150 pumpable composition containing a significant proportion of small particles. With the ore comminuted to particle sizes of less than 0.1 mm~ the proporticn of the cre in the combined slurry advantageously ranges between abcut 10~ and 40% by weight of the solids.

More particularly~ the coarse coal fraction may :; .
be admixed with an ore slurry having a density of about 2 g/cm3 with only a minimum of supplemental water added~
e.g. about 10% by weight. This ore slurry then ac~s as a carrier vehicle for the coal floating thereon. The float-ing coal~ however~ may lead to a more intense wear of the upper wall portions of the pipeline; that drawback can be .
avoided~ pursuant to a further feature of the invention~
by making the density of the ore slurry substantially equal to that of the coal~ i.e. about 1.4 gicm3, whereby virtu-ally all solids remain suspended in the liquid medium and their abrasive effect upon the conduit walls is minimized.

The simultaneous tr-~nsportation of ore and coal -~ ~ through a common pipeline eliminates the need for a freq-uent changeover from one component to the other in addition - to improving the efficiency of the pumping operation.
After preliminary drying by mechanical means~ the two com-ponents can be readily segregated by virtue of their differ-ent specific densities. Furthermore~ with the particle size of the ore not exceeding 74 microns and the smallest coal particles measuring not less than 100 microns~ such segregation can also be easily carried out by screening.

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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of transporting comminuted coal with particle sizes of less than 3 mm to a remote coking station, comprising the steps of:
separating a fine-grain fraction with particle sizes below 0.4 mm from a remaining coarse fraction;
pumping said coarse fraction in a slurry through a hydraulic pipeline to said coking station;
recovering said coarse fraction from said slurry at said coking station;
mechanically dewatering the recovered coal particles;
shipping the separated fine-grain fraction in a dry state to said coking station, said dry state being defined by a water content of substantially 6%;
recombining said fine-grain fraction with the recovered and dewatered coarse fraction at said coking station to form a mixture with a water content of substantially 8%, said fine--grain fraction accounting for at least one fifth of said mixture; and subjecting said mixture to a coking process.

2. A method as defined in claim 1 wherein said slurry is formed from water and a comminuted noncarbonaceous solid carrier, with a density of substantially 1.4 grams per cm3.

3. A method as defined in claim 2 wherein said carrier is an ore.

4. A method as defined in claim 1, 2 or 3 wherein the separated fine-grain fraction is shipped to said coking station by rail.